Electrowetting is a microfluidic phenomenon that modifies the shape of a liquid in relation to a surface by applying an electrical field, e.g. by applying a voltage across two electrodes. For example, if the surface is hydrophobic, the electrical field causes a change in the shape of the liquid that appears to change the wetting properties of the hydrophobic surface. If the fluid(s) in an electrowetting cell and some of the wall(s) around the fluid(s) in a well are sufficiently transparent, the electrowetting cell may be used as an electrically controllable optic. Such optics have recently been the subject of a widening scope of light processing applications, such as variable lenses, variable prisms, optical switches, displays, etc.
Electrowetting lenses provide controllable beam shaping. There have been proposals to develop variable optical prisms using electrowetting cell arrangements. An electrowetting optic may have various different shaped structures, e.g., round, square or rectangular. The overall working principle for either beam shaping or steering is the same—the voltage applied across the dielectric layer attracts or repels the conducting liquid so as to change the wetting area of the cell and thus the shape of the liquid(s) in the cell.
Constructs for electrowetting optics have typically used one or more control channel electrodes. In some examples, each of the control channel electrodes are longitudinally formed to span an entire height of a lateral side wall of the well with longitudinal channel gaps formed between. A common electrode is located, e.g. on or through an end plate, to contact the conductive fluid in the well. The control channel electrodes can be separately controlled with different analog voltages with a waveform to vary the amplitude to drive a conductive fluid further up or down the side wall of the well. Unfortunately, portions of a specific control channel electrode cannot be driven with different waveforms, meaning the exact same waveform is applied to the entire height of the side wall area or region associated with the specific control channel electrode. Amplitude control also typically requires varying higher driving voltage levels, which necessitates channel-to-channel electrical isolation, for example, using a transformer which is bulky, expensive, and slow.
Prior constructs for electrowetting optics typically use complex capacitive compensation techniques due to hysteretic effects and capacitive drift in-which the conductive fluid does not wet to the exact same location in the electrowetting cell even when the same driving voltage is applied. With amplitude controlled waveforms, a capacitive monitoring system monitors capacitance of the control channel electrodes for changes in expected capacitance levels due to these inherent effects. As capacitance of the control channel electrodes increases or decreases, the capacitive monitoring system adjusts the amplitude of the driving voltage accordingly.